“A Heinrich event is a phenomenon in which large armadas of icebergs break off from glaciers and traverse the North Atlantic.” — Commons
“Consider the situation during past ice sheet disintegrations. In melt-water pulse 1A, about 14,000 years ago, sea level rose about 20 meters in approximately 400 years (Kienast et al., 2003). That is an average of 1 meter of sea level rise every 20 years.” — Dr. James Hansen
(Many glaciers along the periphery of Greenland have passed the point of no return. In other words, at present temperatures, these glaciers will completely melt. In the past, such major melting events have released ‘armadas of icebergs’ into the North Atlantic in instances called Heinrich Events. Video source: Chasing Ice.)
As a result, Greenland is producing more icebergs. And this year, it appears that this glacial melt acceleration combined with a very powerful storm to flood the North Atlantic with the bergs at a hither-to unprecedented rate.
(This week, a massive swarm of icebergs that calved from Greenland and entered Baffin Bay have been kicked into the North Atlantic by a powerful storm system. To be clear, this is the kind of thing you’d expect at the start of a Heinrich Event. Image source: U.S. Coastguard.)
Right now, no one wants to make the conclusion that we are starting to enter a Heinrich Event. Or worse — that the present rate of warming at 30 times faster than at the end of the last ice age is rapidly putting us in peril. But the geological evidence for just such an event was a proliferation of ice-rafted boulders from swarms of icebergs that subsequently melted and dropped their rock loads onto the sea floor of the North Atlantic. Heinrich Events are triggered by rapid glacial melt and destabilization of Greenland and Antarctic glaciers as warming airs and waters force the great ice masses past key tipping points.
“[Greenland’s] peripheral glaciers and ice caps can be thought of as colonies of icethat are in rapid decline, many of which will likely disappear in the near future. In that sense, you could say that they’re ‘doomed [emphasis added].’”
… it’s starting to become clear that we’ve probably already started to release this particular ‘climate monster in the closet’ on an unsuspecting and ill-informed world.
(Greenland has numerous estuaries in which warming ocean waters meet with sea fronting glaciers. During recent years, these glaciers have been disgorging ice bergs at increasingly rapid rates. The image above shows icebergs being released from Greenland glaciers during the intense warming event of 2012. Image source: Lance-Modis.)
Heinrich Event in the Human Context
Large outbursts of ice from Greenland’s glaciers into the North Atlantic in a Heinrich Event produce multiple effects. First, the floods of ice and related fresh water push rates of sea level rise higher. At the end of the last ice age, rapid releases of glaciers from Greenland and Antarctica resulted in as much as 1 meter of sea level rise every 20 years. But it’s worth noting that the present rate of warming is about 30 times faster than at the end of the last ice age. So the potential rapid sea level rise risks related to human-forced climate change are considerable.
Second, the icebergs and fresh water floods are likely to disrupt ocean current circulation. This, in turn, makes the North Atlantic a much more stormy and violent place. The cold water produced by the icebergs and fresh water melt creates an atmospheric and oceanic cool zone that runs headlong into warming waters and airs issuing north from the tropics. And it is the collision of extreme hot and cold that often produces the most destructive of weather systems.
(Rapid glacial destabilization and related sea level rise appears to occur when warming exceeds 1.5 to 2.5 degrees Celsius above the longer term base temperature. Meltwater pulse 1A [above] occurred when temperatures warmed about 2 C above the ice age average. The present departure from 1880s averages is currently 1.2 C and we are rapidly approaching the 1.5 C threshold. Image source:Meltwater Pulse 1A.)
The same fresh water and iceberg release that increases regional and hemispheric storm potential also harms ocean health. For when downwelling of cooler, northern currents cease and fail to provide oxygen to the deep ocean — the ocean stratifies, loses a portion of its life-giving oxygen, and starts to produce more and more anoxic dead zones. Ocean circulation interruptions due to Heinrich Events can be relatively brief (on geological time scales) — as has likely been the case at the end of the last ice age during the melt toward the present interglacial — or long-lasting. In the long lasting instance of ocean stratification, bottom water formation is thought to shift to the Equator. In the Earth’s deep past, such events are identified as a primary trigger for ocean mass extinction events or even transition points for a deadly Canfield Ocean state. But you have to shift to an ice-free world at about 6 + degrees Celsius warmer than present to get to the start of that state — a proposition that is now entirely within reach if we continue on the present and ill-fated expedition of continued fossil fuel burning.